Here is a link to Microsoft's Security Advisory on this issue. Be sure to read it for yourself, but basically there are emails circulating that tell you to press the "F1" key, (Help). If the user does this, it could download code that the computer thinks is a help file, but is really malware (virus). Basically, you should always be wary of emails that ask you to do something on your computer.

This is a summary of the issue from their website. Only certain systems are affected. You should contact Microsoft directly for a patch when it is available.

The vulnerability exists in the way that VBScript interacts with Windows Help files when using Internet Explorer. If a malicious Web site displayed a specially crafted dialog box and a user pressed the F1 key, arbitrary code could be executed in the security context of the currently logged-on user.